This invention relates to electromagnetic actuator assemblies and in particular to novel improved linear voice-coil assemblies adapted for reciprocating magnetic transducer means relative to magnetic recording surfaces.
Workers know that computers today commonly employ magnetic disk files for recording and storing data. Disk files have the advantage of facilitating data transfer at randomly selected address locations (tracks) and without need for a "serial seek" as with magnetic tape. Such transducers must be reciprocated very rapidly between selected address locations (tracks) with high precision; i.e., the system must move a transducer between locations very quickly and with high positional accuracy between closely-spaced track addresses. This constraint becomes understandably tricky as track density increases.
Disk file systems commonly mount a transducer head on an arm carried by a block that is supported by a carriage. This carriage is usually mounted on tracks for reciprocation by an associated actuator. This invention is concerned with improving the efficiency of such actuators; and particularly with improving linear "voice-coil" positioners.
Known Positioners:
The acutators commonly used with magnetic disk files are subject to some exacting requirements. For instance, these systems typically involve a stack of several magnetic disks, each with many hundreds of concentric recording tracks with a head-carrying arm typically provided to access each pair of opposing disk surfaces. This arm will typically carry two to ten heads, each to be reciprocated over a stroke excursion of about one inch to position its heads adjacent a selected track. Thus, it will be appreciated that such applications require a high positioning accuracy together with very fast translation (to minimize access time--a significant portion of which is used for head positioning).
Since it is critically important for an actuator system to move a transducer very rapidly between data locations and do so with high positional accuracy between closely-spaced track addresses, this constraint becomes ever more burdensome as track density increases--as is presently the case. Fast access allows a computer to process data as fast as possible--computer time is so expensive that any significant delay over an extended period can inflate costs enormously. [Note: "transition time", during which heads are moved from track to track, is "dead time" insofar as data processing is concerned.]
The trend now is toward ever higher track density, with increased storage capacity and decreased access time. Of course, as track density rises, closer control over the actuator mechanism is necessary to position transducer heads accurately over any selected track, lest signals be recorded, or read, with too much distortion, and without proper amplitude control, etc. An object hereof is to improve control of head positioning.
Computer manufacturers typially set specifications that call for such inter-track movements within no more than a few milliseconds. Such high speed translation is most demanding on actuators; it postulates a powerful motor of relatively low mass (including carriage weight) and low translational friction. Another requirement for such head positioners is that they exhibit a relatively long stroke (several inches) in order to minimize the number of heads required per disk.
The prior art discloses many such positioner devices, including some intended for use in magnetic disk memory systems: e.g., see U.S. Pat. Nos. 3,135,880; 3,314,057; 3,619,673; 3,922,720; 4,001,889; 3,544,980; 3,646,536; 3,665,433; 3,666,977; 3,827,081; and 3,922,718 among others.
Voice Coil Motors:
Workers in the art are familiar with linear magnetic actuators, especially those adapted for reciprocating magnetic transducers relative to magnetic disk surfaces or the like. Such an actuator is the well-known voice coil motor (VCM, or moving coil actuator arrangement). This structure will be recognized as comprising an E-shaped magnetic structure including a central core along which a moving coil is adapted to be movably mounted. "Working flux" circulates through the magnet, traverses a gap, between pole pieces and a core, and is intercepted by the coil. When the coil is energized with a prescribed electric current and cuts a certain flux (prescribed flux density B and current i in coil of length L yields certain force, F=BLI, it will be induced to move as indicated by the arrow. The direction of motion will depend on the polarity of the current relative to the flux, as known in the art.
The "voice coil" motor (VCM) comprises a solenoid like those used to drive an audio speaker. In disk drives, magnetic read/write heads are commonly carried by a carriage driven by a VC motor including a mobile electric coil positioned in a magnetic field and fed by a current of selected intensity and polarity. This magnetic field is typically established by permanent magnet means disposed about the movable coil.
Such a VC linear positioner can exhibit certain disadvantages--for example: undesirably large mass and associated high power requirements; a great burden is placed upon the power requirements to provide maximum acceleration. Such VC actuators are not particularly efficient in converting electrical power. This invention is intended to improve power-efficiency and to control the performance of such VC positioners.
Such actuators commonly experience problems with "eddy currents". Eddy currents impress a "drag" on the actuator, retarding it with a magnitude proportional to velocity. A feature hereof is to enhance eddy current drag, so that it functions as a brake during high velocity, reducing such to a safer level (e.g., here from about 90+ ips to 70-75 ips); particularly by increasing structure resistance (e.g., with a gapped-ring and narrow-rib housing).
In accordance with one salient aspect of the present invention, such a transducer positioner is formed to exhibit braking eddy-current-drag (E-C drag) at unduly-high speeds.
Thus, one object of this invention is to provide the mentioned and other features and advantages. Another object is to teach the use of eddy-current to control positioning of heads in a disk drive. Another object is to provide head actuators for disk drives wherein braking eddy-current-drag is enhanced. Yet a further object is to teach the advantageous use of such transducer actuators in disk drive assemblies.
Another object is to provide a visco-elastic coupling of a coil-drum structure to a carrying structure. A further object is to do so using a thin bonding tape.